Furuno GP-1850WDF - Manual (Page 28)

2. VIDEO SOUNDER OPERATION
2-12
Surface noise/Aeration
When the waters are rough or the boat
passes over a wake, surface noise may
appear near the zero line. As surface
turbulence is acoustically equivalent to
running into a brick wall, the bottom echo will
be displayed intermittently. Similar noise
sometimes appears when a water
temperature difference (thermocline) exists.
Different species of fish tend to prefer
different temperature zones, so the
thermocline may be useful to help identify
target fish. 200 kHz tends to show shallow
thermoclines better than 50 kHz.
In rough waters the display is occasionally
interrupted due to below-the-ship air bubbles
obstructing the sound path. This also occurs
when the boat makes a quick turn or
reverses movement. Lowering the picture
advance speed may reduce the interruption.
However, reconsideration of the transducer
installation may be necessary if the
interruption occurs frequently.
Surface noise
Caused by
aerated water
Thermocline
Surface noise/aeration